1. Field of the Invention
The present invention relates to a display, and more particularly, to a circuit for driving a display of a low power consumption.
2. Background of the Related Art
Recently, passing ahead CRTs (Cathode Ray Tubes) that have been used the most widely, the flat displays, shown up starting particularly from the LCD (Liquid Crystal Display) at the fore front, are developed rapidly in the fields of PDP (Plasma Display Panel), VFD (Vacuum Fluorescent Display), FED (Field Emission Display), LED (Light Emitting Diode), EL (Electroluminescence), and the like.
Because the foregoing displays of a current driven type have, not only good vision and color feeling, but also a simple fabrication process, the displays are widening fields of their applications.
However, the display of a current driven type consumes more current both at the display and a driving circuit thereof as a panel of the display becomes larger. Moreover, the display of a current driven type requires more current for obtaining a desired luminance as a resolution of the display of a current driven type becomes higher because a time period allowed for driving becomes shorter due to a physical quantity required for the display.
Currently, despite the unfavorable characteristics in a response time, an angle of view, the color feeling, and the like, the major reason the LCD is used the most widely is that the LCD has a very small power consumption.
Of course, though the power consumption of the LCD is not small when the back light is taken into account, recently, the LCD of a transflective type, or a reflective type, that permits to dispense with the back light, is employed.
Recently, an organic EL display is paid attention as a flat display that occupies a small space following fabrication of large sized display. FIG. 1 illustrates a related art organic EL driving circuit.
Referring to FIG. 1, the related art organic EL display panel driving circuit is provided with a power source Vdd for applying a voltage to elements, a data driving part of a PMOS for controlling a current from the power source to an anode of an light emitting device 2 in response to a data signal, a data sink part 3 of an NMOS, a scan driving part 4 of an NMOS for making a cathode voltage from the light emitting device 2 conductive in response to a scan signal, and a scan controlling part 5 of a PMOS for applying an inverse voltage to the scan driving part 4.
The other side of the scan driving part 4 is connected to the ground, directly. The data signal and the scan signal applied to the data driving part 1 and the scan driving part 4 respectively are controlled by the controller (not shown).
The scan controlling part 5 has a power supplied from the Vpp, an inverse voltage, and is connected to a cathode of the light emitting device 2. The inverse voltage serves to prevent cross talk of the light emitting device 2.
The foregoing display has smaller power consumption in comparison to the CRT, no distortion at edge parts, and permits to fabricate an extra thin display. Moreover, the foregoing display permits fabrication of a large sized screen because it is robust in comparison to the LCD and has a wider angle of view owing to self-luminescence and a good responsive characteristics, has a wide range of service temperature of −40°–+70°, permits to select a wide variety of colors without restraints, and is operative even with a voltage as low as 15V.
However, a major reason the LCDs, which have more unfavorable characteristics than the displays of a current driven type with the foregoing advantages, are employed in portable information devices and the like more than the displays of a current driven type is that the organic ELs have a power consumption greater than the LCDs.
Since the great power consumption of the portable information terminal devices rises as a great problem as use of the portable information terminal devices increases, the problem acts as a factor that restricts use of the display of a current driven type.
However, in general, though the power consumption of the display of a current driven type is a few times of the LCD, this simple comparison has no meaning. That is, if the back light of the LCD is included, there is not so much difference of power consumption between the LCD and the display of a current driven type.
Moreover, if the power consumption of the display of a current driven type is reduced by approx. half from a total level, a total power consumption of the display of a current driven type can be reduced to a level almost the same with the LCD.